Foil-filled photoflash lamps



Sept. 27, 1955 A. FREEMAN FOIL-FILLED PHOTOFLASH LAMPS Filed Sept. 1, 1954 2,718,771 FOIL-FILLED PHOTOFLASH LAMPS George A. Freeman, East Orange, N. J., assignor to Westmghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application September 1, 1954, Serial No. 453,649

3 Claims. (Cl. 67-31) This invention relates to foil-filled photoflash lamps and the manufacture thereof and, more particularly, to such of an improved and simplified construction.

There is disclosed in patent application of Russell H. Atkinson and Norman C. Beese, S. N. 453,639, filed concurrently herewith, titled Foil-Filled Photoflash Lamps and Igniter Therefor, and assigned to the present assignee, a foil-filled photoflash lamp in Which the igniter consists of a primer coated over a metallic lead, which lead has a thin coating of dielectric, preferably consisting of its own oxide; As disclosed therein, this oxide coated lead insures against a low resistance contact between the primer and the metallic portion of the lead and also insures that the breakdown voltage of the material between the lead and the primer will not be sufliciently large as to prevent a spark discharge being initiated, which spark discharge is needed to fire the lamp.

Such a construction as disclosed in the Atkinson and Beese application is an improvement over copending application of C. M. Rively, Serial No. 358,415, filed May 29, 1953, and owned by the assignee of the present application.

The structure as disclosed in the Atkinson and Beese application requires that the lead on which the primer is coated be inserted in the plastic base of the photofiash lamp in a separate operation. Also, care must be taken to insure that a portion of the lead will serve as a contact electrode through which a potential may be applied to fire the lamp.

It is the general object of this invention to provide a foil-filled photoflash lamp in which the primer lead is constructed as an integral part of the lamp base.

It is another object of this invention to simplify the manufacture of photoflash lamps so that the bases and primer leads are fabricated in one step. The lamp bulbs may be exhausted and gas-filled simultaneously with the connection of the metal bases thereto by means of a plastic material held in the metal bases.

It is a further object of this invention to provide a photofiash lamp of simplified construction in which the neck of the bulb is embedded in an annular pool of plastic held in a metal base and disposed around an upstanding prong or embossment of said base.

For a better understanding of the invention, reference should be had to the accompanying drawing wherein:

Fig. l is an axial sectional view of a lamp embodying my invention, a circuit for igniting such a lamp being indicated diagrammatically.

Fig. 2 is an elevational view, with parts in axial section, of apparatus which may be employed for softening the plastic filling in a base, exhausting, gas filling, and embedding the lower edge of a bulb neck in plastic in such base.

Fig. 3 is an expanded, fragmentary, elevational, sectional View of the coated prong or tip portion of the base.

For a better understanding of the invention reference should be had to the accompanying drawing wherein, in first considering Fig. 1, there is shown a photofiash lamp j nited States Patent 2,718,77I Patented Sept. 27, 1955 21 comprising an envelope or bulb 22 of radiation-transmitting, transparent or translucent material such as glass. The edge of the neck 23 of said bulb 22 is embedded in an annular pool of plastic 24 held in a metal base 25. Instead of a lead for the lamp of the present embodiment, the central portion of the metal base 25 is formed with an upward embossment, indicated at 26, forming a relatively sharp prong 27 centrally disposed with respect to the sides of the cup-shaped base 25. The prong 27 projects in the same direction as the sides of the base leaving an annular cavity therearound in which the plastic material 24 is disposed.

The interior of the base 25, or at least the portion of the prong 27 which extends above the plastic 24, is prefer-.

ably coated with porous dielectric material 35 of any de-. sired character. This dielectric material is desirably provided by forming the base 25 of aluminum, or with an inner aluminum surface, which is oxidized to form an adherent coating of porous aluminum oxide. On the tip of the prong 27 is disposed a mass of primer material 28, which may be conventional such as a paste formed of zirconium powder, or other suitable metal, and an oxidizing agent. This is shown in Fig. 3. The bulb 22, the neck of which is cemented to the base by the plastic material 24, encloses a mass of combustible material 29, such as shredded aluminum and/or magnesium in an atmosphere of oxygen or other combustion-supporting gas, such as suitable oxides of nitrogen, for example.

As a specific example, the upward embossment 27 of the cup-shaped metal base 25 may extend /8" into the bulb beyond the plastic material 24. The porous aluminum oxide layer over the exposed tip may have a thickness of 1 mil. The thin layer of primer over the insulat ing or dielectric oxide layer need only be used in rela-' tively small amounts, for example, 5 mg. Such a primer may consist of a mixture of zirconium powder and 10% potassium perchlorate. The shredded combustible 29 may be shredded aluminum in amount of 35 mg., for example. The combustion-supporting gas contained within the bulb may be oxygen at a pressure of 600 mm.

Other material may be used as the primer such as a mixture of magnesium plus an oxidizer or nitrostarch plus aluminum and an oxidizer, for example.

The wiring diagram of Fig. 1 indicates how the lamp there illustrated may be fired. In this diagram, the reference character 31 represents a source of power, which may be a 22 /2 volt hearing aid dry cell battery. Connected to the battery is a resistor 32, of preferably about 10,000 ohms, and a condenser 33, of preferably about 50 microfarads capacity, said condenser being across the battery terminals with the resistor in series.

The condenser terminals are in turn connected through a switch 34 to the primary winding 36 of a step-UP transformer 37. The secondary winding 38 of said transformer has one terminal connected to a terminal of the primary winding 36, and the other terminal connected to the base 25 of the lamp 21. With this arrangement, the condenser is slowly charged through the resistor 32 and is in condition for delivering a desired surge of electrical energy to the primary winding 36 of the transformer upon closing the switch 34.

The ratio between the turns of the primary and secondary windings is desirably such that a potential of from 10,000 to 20,000 volts is delivered to the base 25 on closing the switch 34, to thereby produce a discharge between the inner end of the prong 27 and the primer material 28 across the gap between the metal thereof and the primer through the porous insulating material 35, thereby igniting the primer and through it the surrounding cornbustible material 29.

Although I have diagrammatically disclosed means for igniting a lamp embodying my invention, yet practical embodiments of such means are illustrated in Figs. 5 and 6 of the copending application of C. M. Rively, Ser. No. 358,415, filed May 29, 1953, and owned by the assignee of the present application.

A lamp such as illustrated in Fig. l is desirably manufactured using apparatus such as illustrated in Fig. 2. The metal base 25 after shaping by conventional pressing techniques, for example, has a charge of plastic material 24 placed therein. The plastic material desirably employed may be that designated by the trademark Vinnapas. This is a so-called sealing plastic manufactured by Dr. Alexander Wacker, Gesellschaft fiir Electrochemisch Industrie, G. m. b. H., 22 Prinzregentenstrasse, Munich, Germany. This is 45% polyvinyl acetate, 25% powder talc, and 30% microcrystalline wax. Alternatively, the bulb neck may be sealed to the metal base by means of a polymer resin such as an epoxy resin. Such resins are well-known and are characterized by having the epoxide group it a as the polymerizing unit. However, other solid plastic materials which have melting points lower than that of the bulb 22 to which connected, and low enough to permit softening, prior to ignition of the primer 28, may be employed, as by melting and pouring in place.

In applying the porous oxide coating to the prong 27 of the metal cup-shaped base 25, where such base is fabricated of aluminum, an anodizing process may be used, either before or after the annular plastic sealing material 24 is inserted into the base 25. In such an anodizing process, the prong 27 of the metal base is made the anode and an inert electrode the cathode. The electrolyte may be 0.1 molar sulphuric acid. A current of 2-3 amps. at 30 volts is passed for about 15 seconds, after which the prong 27 is withdrawn from the electrolyte, washed with hot water and air-dried. The process as described will produce an oxide coating on the prong of about 1 mil thickness having a breakdown voltage of about 100 volts. As disclosed in the aforementioned Atkinson and Beese copending application, the oxide coating in the case of aluminum should be at least 0.5 mil thick and not over mils thick. The mechanism by which such an aluminum oxide coating operates to promote a spark discharge is discussed at length in the heretofore-mentioned Atkinson and Beese application, but briefly the spark discharge is set up between the base metal of the prong and primer contacting portions of the shredded combustible through rifts or crevices which in effect form pores in the aluminum oxide and through the plurality of pores which are encountered in a thin coating of primer.

While aluminum oxide on an aluminum base metal is preferred and is excellent in such an application as the instant one, other base metals may be oxidized and be very satisfactory. For example, the metal cup and oxide coated prong may be fabricated of nickel and nickel oxide, tantalum and tantalum oxide and titanium and titanium oxide, to mention a few. Alternatively, a dielectric other than an oxide of the base metal may be coated onto the prong, providing of course that such a dielectric has a relatively low breakdown strength to facilitate the setting up of a spark discharge. For example, graphite may be embedded in polystyrene or methylacrylate and coated onto the prong. Also the aforementioned rifts in the oxide dielectric are not necessary provided the dielectric will break down with an applied potential of at least 100 volts and not exceeding 1000 volts. Of course, if the total applied potential is other than the specified 10,000 to 20,000 volts, the permissible breakdown voltage for the oxide dielectric coating on the tip may vary, and the permissible breakdown voltage for such applications may be readily determined by one skilled in the art.

The apparatus of Fig. 12 of the Rively application rei ferred to may serve for applying primer to the prong 27, although it will be understood that such primer may be applied in any desired manner as is well understood by those skilled in the art.

After application of the paste primer 28 to the prong 27 over the insulation 35, the former is allowed to dry and the mount so constructed is then reversed in position. The base 25 is inserted in a cup 59 mounted on the upper end of a reciprocable rod 61 and carrying a light spring 62 in its interior. The spring 62 resiliently urges a disk 60 into engagement With the bottom of a supported base 25. The cup is disposed in an exhausting and gas-filling chamber 63, which for the purpose is connected to an exhaust and gas-filling system, as by means of a pipe 64. Leakage between the rod 61 and the lower wall of the chamber is prevented by means of a sealing bellows arrangement 65, desirably the so-called sylphon type.

In the chamber 63 is mounted a coil of oxygen-resisting nichrome or other heating wire 66, surrounding the cup 59. Leads 67 and 68 connect the wire 66 to a source of power by energizing the same to quickly soften the plastic material 24 in the base 25, without igniting the primer 28, while said base is resiliently supported in the cup 59. The chamber 63 opens upwardly and is partially closed by a rubber or other resilient cover 69, apertured as indicated at 71 to receive the neck 23 of the bulb 22, while nesting with the main or bulbular portion thereof to provide an air-tight engagement.

The manner of operating the apparatus for uniting a base to a bulb after exhausting and gas-filling is as follows: A mount comprising a plastic-holding base 25 and an oxidized or otherwise insulated prong 27, carrying a mass of priming material 28, is placed with the base resting on the spring 62 and disposed in the cup 59. A bulb 22 carrying combustible material of conventional character 29, for example, is then placed over the primer 28 to close the aperture 71. The air in the chamber 63 and connected bulb 22 is then exhausted, while the coil 66 is energized to soften the plastic material 24.

After exhausting to the desired extent, oxygen or other combustion-supporting gas is introduced into the chamber 63 from whence it passes to the bulb 22. The bulb during the operation is held in place by a suitable chuck 72. When filling gas at the desired pressure has been introduced and the base plastic 24 sufficiently softened, the rod 61 is raised to push the base 25 into sealing engagement with the lower end of the neck of the bulb. The apparatus and formed lamp are then allowed to cool and the lamp removed and replaced by parts of other lamps for a repetition for the operation.

Although a preferred embodiment has been disclosed, it will be understood that modifications may be made within the spirit and scope of the invention.

I claim:

1. A photoflash lamp comprising a radiation-transmitting bulb with a neck, a metal cup holding sealing cement, and with a central indentation projecting in the same direction as the side walls of said cup, the tip of said indentation projecting above the free surface of said cement, a dielectric coating on said tip, a primer supported on said coating, the edge of the bulb neck being embedded in said cement around said indentation, shredded combustible material in said bulb, part of which is contacting said primer, and a combustion-supporting atmosphere in said bulb.

2. A photoflash lamp comprising a radiation-transmitting bulb with a neck, a metal cup holding sealing plastic, and with a central conductive prong in said cup, the tip of said prong projecting above the free surface of said cement, a dielectric coating on said tip, primer supported on said coating, the edge of the bulb neck being embedded in said plastic around said prong, shredded combustible material in said bulb, part of which is contacting said primer, and a combustion-supporting atmosphere in said'bulb.

3. A photoflash lamp comprising a radiation-transmitting bulb with a neck, a metal cup holding sealing plastic and with a central relatively sharp embossment, the tip of which is exposed above the free surface of said plastic, said cup being formed of aluminum, the exposed portion of said tip being oxidized, a primer on said oxidized tip portion, the edge of said bulb neck being embedded in 'said plastic around said tip, shredded combustible material in said bulb, part of which is contacting said primer, and

a combustion supporting atmosphere in said bulb.

References Cited in the file of this patent 

